Technically a lion wouldn't be able survive on just bugs, no matter how much protein they have. Simba at some point realistically would have become malnourished and may have been forced to eat other animals.
Rafiki's design seen throughout the promotional materials firmly establish him as a mandrill (as opposed to a baboon), resulting in him being very out of place as mandrills hail from the rain-forests of West Africa, as opposed to the East African Serengeti.
Adult Simba roars atop Pride Rock, but the sound he makes is the typical Hollywood beefed-up roar rather than an actual lion vocalization. He also does the stereotypical wide-mouth yelling posture commonly associated with roaring, but actual full-blown lion roars are produced with the mouth in an almost closed position similar to a howling wolf. However, the roars used are NOT tiger roars, as is often stated. Tiger roars are actually higher-pitched than those of lions.
Simba and Nala would never mate., Given the pride dynamics, there's no way that Simba and Nala aren't related. At the very least, they're cousins, but more likely they're actually brother and sister. So they wouldn't be feeling the love tonight.
Zazu has a combination of features from different horn-bill species of the genus Tockus. His general plumage coloration resembles red-billed hornbills, specifically Tanzanian red-billed hornbills (Tockus ruahae), but his bill features a prominent casque which all red-billed horn-bill species uniquely lack, as well as being an orange-yellow color that is much more commonly found in both Southern and Eastern yellow-billed hornbills (T. leucomelas and T. flavirostris, respectively).
A group of gemsbok (Oryx gazella) are featured in the first teaser trailer even though the species is only found in southwestern Africa rather than the East African setting of the story. The similar and related East African oryx, specifically the beisa oryx (Oryx beisa beisa), would've been a more appropriate choice.
The giraffes seen throughout the promotional materials, specifically resemble the Rothschild giraffe subspecies/ecotype.note Despite these giraffes presently only found in a select few protected regions of Uganda and western Kenya, their historical distribution was wider only a few centuries ago and possibly could've encompassed the Serengeti-Mara region proper alongside their cousins, the Maasai giraffe (G. c. tippelskirchi), which don't appear in any of the footage despite being the most common giraffe in the region.
Adult lions never return to their birth prides. The only males that are allowed to stay around are those that are good breeders. In other words, that aren't related to everyone in the pack - as Simba would have been.
Newborn cubs aren't presented to the pride. While the filmmakers tried to make baby Simba more "realistic" in the new movie by adding blue to his eyes to indicate the blindness cubs are born with, the truth is lionesses seclude themselves with their cubs for at least the first six weeks of their lives.
Scar's cover-up of his murder of Mufasa leaves a gaping hole, he sends Zazu to get the pride for help, and after the stampede, claims to the pride that he didn't reach the gorge in time to help Simba and Mufasa. Zazu is implied to have been exiled from the pride after Scar's take-over (given how the hyenas regularly try to eat him when he shows up), but considering Zazu still clearly regularly visited Pride Rock to relay information, it's a wonder how Scar's lie about not being able to make it to the gorge didn't get exposed by Zazu.
The pride doesn't come to Simba's defense when he confesses responsibility for Mufasa's death, even after he says it was an accident that happened when he was a cub, and Scar backs Simba to the cliff of Pride Rock and gloats to him about the look in Mufasa's eyes before his death. Whereas in the original this was a more private conversation the others didn't hear, in the remake, once Simba turns the tables on Scar, Sarabi asks how Scar saw the look in Mufasa's eyes if he didn't make it to the gorge in time, proving that it wasn't a private conversation. If Sarabi could hear Scar admit he was lying, why didn't she try to step in sooner?